In a power supply system for a three-phase arc furnace (1), comprising at least one furnace transformer (4), the furnace transformer (4) is connected on the secondary side to the three-phase arc furnace (1). On the primary side, the furnace transformer (4) is connected to a three-phase supply mains (3) through an indirect converter (5). The indirect converter (5) comprises at least one rectifier (6) on the mains side, at least one inverter (7) on the transformer side, and an intermediate circuit (8) between the rectifier (6) and the inverter (7). Each phase of the three-phase supply mains (3) is connected to the intermediate circuit (8) through two converter elements (11) of the rectifier (6) in each case. Each primary-side phase of the furnace transformer (4) is connected to the intermediate circuit (8) through two converter elements (2) of the inverter (7) in each case.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A power supply system for a polyphase arc furnace, comprising: at least one furnace transformer whose primary is connected via an indirect converter to a polyphase mains system and whose secondary is connected to the polyphase arc furnace, wherein the indirect converter has at least one rectifier on the mains side, at least one inverter on the transformer side, and a link circuit between the rectifier and the inverter, wherein each phase of the polyphase mains system is connected to the link circuit via two converter elements of the rectifier, and wherein each primary phase of the furnace transformer is connected to the link circuit via two converter elements of the inverter, wherein each converter element of the two converter elements of the rectifier and the two converter elements of the inverter consists of a multistage series circuit of submodules, wherein each submodule of the submodules comprises an energy storage capacitor and self-commutated semiconductor switches, and wherein the self-commutated semiconductor switches in each submodule can be switched independently of the self-commutated semiconductor switches in other submodules in a same converter element and in other converter elements, such that the energy storage capacitor in a respective submodule is bridged or active by means of the self-commutated semiconductor switches in the respective submodule, depending on their switching state.
2. The power supply system according to claim 1 , wherein the self-commutated semiconductor switches in the converter elements are operated such that reactions, which go beyond the balanced load on the phases of the polyphase power supply system with real power, of the phases of the polyphase arc furnace on the polyphase mains system are minimized.
3. The power supply system according to claim 2 , wherein the number of self-commutated semiconductor switches per submodule is two.
4. The power supply system according to claim 2 , wherein the furnace transformer does not have a power factor corrector connected in parallel with it.
5. The power supply system according to claim 1 , wherein a power factor corrector is connected in parallel with the furnace transformer.
6. The power supply system according to claim 5 , wherein the power factor corrector has a number of further converter elements, each further converter element of the number of further converter elements consists of a multistage series circuit of further submodules, each further submodule of the further submodules of which comprises an energy storage capacitor and self-commutated semiconductor switches, the self-commutated semiconductor switches in each further submodule can be switched independently of the self-commutated semiconductor switches in other further submodules in a same further converter element and in other converter elements, such that the energy storage capacitor in a respective further submodule is bridged or active by means of the self-commutated semiconductor switches in the respective further submodule, depending on their switching state, and the self-commutated semiconductor switches in the further submodules are operated such that reactions, which go beyond the balanced load on the phases of the polyphase mains system with real power, of the phases of the polyphase arc furnace on the polyphase mains system are minimized.
7. The power supply system according to claim 5 , wherein the power factor corrector is connected to the primary phases of the furnace transformer.
8. The power supply system according to claim 5 , wherein the power factor corrector is connected to the phases of the polyphase mains system.
9. The power supply system according to claim 1 , wherein a capacitor circuit is connected to at least one of the primary phases of the furnace transformer and to the phases of the polyphase mains system.
10. The power supply system according to claim 1 , wherein each inverter is connected to a maximum of one furnace transformer.
11. A method for providing power to a polyphase arc furnace, comprising: connecting a primary of at least one furnace transformer via an indirect converter to a polyphase mains system and connecting a secondary of the at least one furnace transformer to the polyphase arc furnace, wherein the indirect converter has at least one rectifier on the mains side, at least one inverter on the transformer side, and a link circuit between the rectifier and the inverter, connecting each phase of the polyphase mains system to the link circuit via two converter elements of the rectifier, and connecting each primary phase of the furnace transformer to the link circuit via two converter elements of the inverter, wherein each converter element of the two converter elements of the rectifier and the two converter elements of the inverter consists of a multistage series circuit of submodules, providing for each submodule of the submodules an energy storage capacitor and self-commutated semiconductor switches, and switching the self-commutated semiconductor switches in each submodule independently of the self-commutated semiconductor switches in other submodules in a same converter element and in other converter elements, such that the energy storage capacitor in a respective submodule is bridged or active by means of the self-commutated semiconductor switches in the respective submodule, depending on their switching state.
12. The method according to claim 11 , further comprising operating the self-commutated semiconductor switches in the converter elements such that reactions, which go beyond the balanced load on the phases of the polyphase power supply system with real power, of the phases of the polyphase arc furnace on the polyphase mains system are minimized.
13. The method according to claim 12 , wherein the number of self-commutated semiconductor switches per submodule is two.
14. The method according to claim 12 , wherein the furnace transformer does not have a power factor corrector connected in parallel with it.
15. The method according to claim 11 , wherein a power factor corrector is connected in parallel with the furnace transformer.
16. The method according to claim 15 , wherein the power factor corrector has a number of further converter elements, each further converter element of the number of further converter elements consists of a multistage series circuit of further submodules, each further submodule of the further submodules of which comprises an energy storage capacitor and self-commutated semiconductor switches, and the method further comprises: switching the self-commutated semiconductor switches in each further submodule independently of the self-commutated semiconductor switches in other further submodules in a same further converter element and in other converter elements, such that the energy storage capacitor in a respective further submodule is bridged or active by means of the self-commutated semiconductor switches in the respective further submodule, depending on their switching state, and operating the self-commutated semiconductor switches in the further submodules such that reactions, which go beyond the balanced load on the phases of the polyphase mains system with real power, of the phases of the polyphase arc furnace on the polyphase mains system are minimized.
17. The method according to claim 15 , further comprising connecting the power factor corrector to the primary phases of the furnace transformer.
18. The method according to claim 15 , further comprising connecting the power factor corrector to the phases of the polyphase mains system.
19. The method according to claim 11 , further comprising connecting a capacitor circuit to at least one of the primary phases of the furnace transformer and to the phases of the polyphase mains system.
20. The method according to claim 11 , further comprising connecting each inverter to a maximum of one furnace transformer.
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September 8, 2009
January 13, 2015
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